Reduction in carbon dioxide (CO2) emission from the coal-fired power plants has become a focal point of international efforts for climate control in recent years. Carbon dioxide emission from coal-fired power plants constitutes a relatively large portion (˜40%) of total CO2 emissions. Developing a means to control coal-derived CO2 emission is imperative in this effort; however, the cost for such carbon capture and sequestration (CCS) can be up to 50% of the energy production cost of a coal-fired power plant. A major portion of the penalty for CCS is the energy loss in cooling the flue gas (typically up to 750° C. exiting from the burner) to a lower temperature (100-300° C.), which the CO2 separation system can tolerate. One reported method of reducing the energy penalty for CCS is to separate CO2 at the existing flue gas temperature.
Relatively early studies of CO2 capture with membranes indicated that the cost was 30% higher than the cost of the traditional amine chemical absorption process. The limitations of the studied membrane processes was identified as coming from the high cost of compressing low pressure flue gas and the low purity of the permeate, which resulted in the need for multistage processing to achieve the most economic arrangement for CCS in such systems. Recent analyses show that considerable CO2 removal rates can be achieved with gas membrane separation systems, and the economic competitiveness of such systems in comparison with amine-based systems depends on the characteristics of both of membrane and feed gas. When membrane selectivity and permeability are improved, the CO2 capture and total CCS costs may be reduced by up to 15% compared to the amine process.
CO2 separation using membranes is a topic of great commercial interest with most of the reported membranes operating at relatively low temperatures. From the viewpoints of mechanism of separation and material stability, a growing need exists for membrane materials that are useful at temperatures of 400° C. or above.